Purpose: The aim of this observational study was to determine how participation in organized sports (specifically handball) affect the daily level of physical activity and time spent in front of screen. Methods: 20 children with an average age of 10 years (SD=1), who play handball as an after school activity, participated in the research. Data were taken from 20 subjects, of which 15 were boys and 5 were girls. We monitored the time spent in physical activity, daily number of steps and energy consumption with a wearable device for monitoring physical activity over a period of 14 consecutive days and nights, continuously for 24 hours. Participants wore the watch all the time, and only took it of to charge it or for safety reasons if they were engaged in some other physical activity. In addition to the watch, participants kept a diary in which they recorded the time they spent on the mobile phone, television and computer. Student T-test for dependent samples was used to test for differences in amount of physical activity, number of steps, calorie consumption, and screen time between training and nontraining periods and between the school week and weekend. Results: Children were significantly more active during the week (446±100 min/day), compared to the weekend days (378±82 min/day) (p=0,007), and are more active on those days when there was training (476±105 min/day), compared to the days when there was no training (402±78 min/day) (p<0,001). Analysis also showed a large amount of time that children spend in front of screens. During the weekdays (120±80 min/day), children spent less time in front of the screen compared to weekend days (183±76 min/day) (p<0,001), which can be linked to sedentary leisure time. We obtained similar data for the days when ther was training (111±71 min/day) compared to when there was no training (148±79 min/day) (p<0,001). Conclusion: Through organized sports, we influence the increase in the amount of physical activity among children and adolescents, and thereduction of sedentary behavior, that is, the time children spend in front of the screen. Due to the decreasing amount of time that children spend independently plaing in their free time, it is necessary to introduce them to organized sports, and in this way infuence the increase in physical activity and thereby influence proper development, improvement of health and prevention of diseases.